Soundboards: Thickness and Area

[Delwin D Fandrich]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: October 21, 2003 2:55 PM
Subject: Re: Soundboards: Thickness and Area


>
>
>
> But I still see nothing in this that goes to show that these edge
> patterns have anything to do Chladni patterns. If they are shown to be
> part of a resonant mode, then they are. If they are not part of any
> resonant mode, then they have nothing to do with Chladni patterns.

Then what magical force is drawing the sand to the edges? It's a Chladni
pattern, Richard. Whether you want to accept it or not.


>
> The fact that banging the sound board excites all the modes too some
> degree is not disputed, nor is the fact that judicious use of a hammer
> can lend more support to a given mode including the fundamental. It just
> doesn't seem particularly usual to display these (Chladnis) with sand in
> this fashion and perhaps that is because the resulting patterns are so
> poorly defined. It does seem usual to use this method of excitation for
> computer modal analysis as discussed by Wogram.

You're right, it's not the usual method of exciting resonances in a
soundboard to observe Chladni patterns. It is, however, one way of doing so
if your area of primary interest is the fundamental mode of vibration.


>
> It is not given by any of this that Steingræber is (consciously or
> otherwise) exciting, viewing, and manipulating the first, or any
> particular mode at all. If he is, then great. But since he himself says
> it has nothing to do with these, and since I've seen no reason to doubt
> him, I'll delay accepting any position to the contrary.

If you reported accurately, he said it was not the same as a modal
analysis. That is correct. A modal analysis is a far more complex affair
and you seem determined to confuse the two. What Steingraeber is doing
represents a simple way of observing where sand goes when the physical
motion in a vibrating panel knock it around and it migrates to a place of
relative stability. In other words, it settles to a stationary node. That's
what Chladni patterns do.


>
> As far as I can see, the only real moment of contention is that which
> was from the beginning of this little round. That is, whether or not
> Steingræbers edge patterns have anything to do with Chladni patterns or
> not. If they conform to a resonant mode, then they do. If they do not
> conform to a resonant mode...they they have nothing to do with Chladni.
> Simple test to find out. Run the fundemental resonant frequency and find
> out.

That's right. You wrote that a Chladni pattern was not a Chladni pattern.

Sorry, Richard. I'm not the one needing convincing. You'll need to get your
own hands dirty for this one. I've already been there.

Del